This invention relates to a method of co-ordinate registration for Over-the-Horizon Radar.
The principle of Over-the-Horizon Radar (OTHR) is to radiate high frequency (HF) power via the ionosphere to long ranges then analyse the backscattered return signal for target and environmental information. The backscattered return data is processed over four domains; namely, azimuth, slant range, Doppler and time.
The location of targets is determined from the signal delay time and the directional characteristics of the radar receiving array. The signal delay time provides an indication of the length of the radar path which gives a slant or group range. For accurate determination of a target's position transformation from slant range to ground range and from radar direction to actual direction must be performed. This transformation is known as co-ordinate registration.
The transformation is complicated by the fact that the ionosphere does not act as a simple reflector. The nature of the ionosphere varies considerably over time and space so that it is not easy to determine the location from which a returned signal has come. It is necessary therefore to provide some method by which return signals can be correlated with a true geographical map. The present invention is directed to this problem.